1. Field of the Invention
The present invention relates to a method and device for inspection or examination of a joint between a steel shaft and a piece to be joined to the steel shaft of a composite camshaft.
2. Description of the Prior Art
A composite camshaft having a steel shaft and a piece joined to the shaft is well known. In the composite camshaft, an element such as a cam, a journal, a gear and a fitting means for a spanner is constructed of a part independent of the shaft of the composite camshaft and then the piece is fitted to the shaft and is integrally joined to the shaft. Japanese Utility Model Publication No. 51-7367 discloses a composite camshaft of this kind in which at least one of a cam and a camshaft is constructed of a sintered metal and then is integrally joined to the steel shaft through diffusion by sintering.
In a composite camshaft, the piece to be joined to a shaft is not limited to a sintered metal and may be constructed of steel. In the case the piece is constructed of steel, the steel piece is usually joined to the steel shaft through braze welding or solder welding. In such a composite camshaft, the joint between the piece with the shaft should be examined and be confirmed to be of high quality and strength.
As a method for examination of the joint of the composite camshaft there is presently utilized a destructive examination in which the composite camshaft is cut and the exposed surface is examined by sight. However, such a destructive examination requires much time and expense.
Recently, an ultrasonic examination has been applied to the examination of the joint of a composite camshaft in which a probe of an ultrasonic search unit is moved along the joined piece with the probe in direct contact with the outside surface of the joined piece. However, such an ultrasonic examination requires a considerable amount of time and results in the consumption of the probe and therefore, is not deemed economically appropriate. In addition, since the ultrasonic examination is applied from outside of the composite camshaft and since the distance from the outside surface of the joined piece to the joint varies in the circumferential direction of the cam due to the radial distance difference between the base circle portion and the cam nose of the cam, the quality of the examination is of a low grade. Further, since the ultrasonic wave beams do not transmit straight at the surface of the cam nose in the case of the cam, the examination of the portion of the joint corresponding to the cam nose has been impossible.